274 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



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Car driven 

 through tracer. 



Truck driven 

 through tracer 



Car driven 

 past tracer 



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10 

 VEHICLE SPEED, mph 



100 



Fig. 24 Rates of tracer particle resuspension caused by vehicle passage over an asphalt 

 road. 



greater when the vehicle was driven through the tracer lane than when driven on the larie 

 adjacent to the tracer lane. 



Resuspension caused by truck passage througli a cheat grass area was also measured 

 (Sehmel, 1976c; 1977b). Results are shown in Fig. 26 along with resuspension rates from 

 the asphalt road. Truck-caused resuspension from the cheat grass area was always less 

 than that from the asphalt road. This decrease is attributed to the protective action of 

 cheat grass in hindering truck-generated turbulence from reaching the ground and 

 resuspending the tracer. 



Resuspension from the cheat grass area decreased for truck speeds from 5 to 30 mph. 

 This decrease is attributed to the sequence of experimental truck speeds. The initial truck 

 speed was 5 mph. Apparently the relatively larger resuspension rate at 5 mph was caused 

 by the most readily resuspended particles being removed from the cheat grass. In 

 succeeding experiments at increasing truck speeds up to 15 mph, and possibly 30 mph, all 

 readily resuspended tracer was removed from the cheat grass foliage. When the truck 



